H2 adsorption on coal considering the nanopore size distribution: Insight from the lattice density functional theory

Hydrogen (H 2 ) storage in coal seams is a potential option for large-scale subsurface energy storage, especially in abandoned or unmineable reservoirs. Here, supercritical H 2 adsorption in coal was investigated by combining pore-structure characterization, high-pressure adsorption experiments, and lattice density functional theory (LDFT) modeling. Micropores (<2 nm) dominate the total pore volume, with pores around 0.6 nm providing the largest contribution to H 2 uptake. The LDFT model reproduced the adsorption isotherms with high accuracy ( R 2 ≥ 0.9984) and out performed conventional models by explicitly accounting for pore-size-distribution and fluid-solid interactions. At high pressure, absolute adsorption was 1.4–1.7 times higher than excess adsorption, indicating that metric selection strongly affects storage-capacity estimates. A strong positive correlation was observed between H 2 excess adsorption and micropore volume and between fixed carbon content and vitrinite reflectance. Moreover, this study highlights the crucial role of micropores, fixed carbon content, and thermal maturity in enhancing H 2 storage capacity, providing a theoretical basis for evaluating coal as a viable underground H 2 storage medium.